Performance of turbo codes on frequency-selective Rayleigh fading channels with joint data and channel estimation

Various turbo codes together with π/4 DQPSK modulation are investigated for frequency-selective Rayleigh fading channels. The soft output Viterbi algorithm (SOVA) is selected for equalising multipath fading channels so that both reliability information can be available for turbo decoding and the channel impulse response can be effectively estimated. To keep the receiver´s complexity low, turbo codes are, built from a simple recursive systematic convolutional code with constraint length K=3. The number of channel estimators in the SOVA and the number of iterations to be performed in turbo decoders are also kept small. Simulation results for different mobile speeds and different frame lengths are obtained and it is shown that when the frame size is long enough, turbo codes can significantly outperform a convolutional code of constraint length K=6